Supercapacitor, is also called electrochemical capacitor, has much higher energy density than conventional capacitor but is still lower than batteries. The charge storage of supercapacitor mainly depends on the electrochemical reaction or the electrical double-layer on the electrode surface, and it possesses advantages of rapid charging-discharging, long cycle life, good stability, widely range of operation temperature, simple circuit, reliability, and environmental friendly. Currently, supercapacitors have been commercially available for wide applications, e.g., personal consumer electronics, electric vehicles, flexible electronic display and aerospace, etc. However, the energy density of the existing supercapacitor is still much lower than battery (e.g., lithium battery). On the contrary, battery (e.g., lithium ion battery) possesses higher energy density but low power density, which requires a long time to charge/discharge, and has safety risks.
Therefore, it's essential to develop a novel supercapacitor with both high energy density and high power density to substantially solve the serious problems in important applications such as electric vehicles which require both high energy density and power density and short charge time for the energy storage and conversion devices. No matter whether it is the battery or the supercapacitor, the key to improve its energy density and power density is to choose proper electrode material and electrode structure. The components and micro nanostructure of the electrode material are decisive factors for energy conversion and storage.
Currently, the electrode material of the supercapacitor mainly uses carbon with high specific surface and/or electrochemically active materials such as metal oxides and conductive polymers. In addition, some metal hydroxides, metal sulfides and mixed metal oxides are also used as the electrode material of the supercapacitor. Although these materials exhibit superior specific capacitance (i.e., charge storage capacity) and high energy density, their power density is poor, and their energy density is low under high charge-discharge rate.
In view that no prior art has ever disclosed a battery or a capacitor that possesses both high power density and high energy density and has both battery and capacitor characteristics, there is a need to develop a completely novel conceptual battery type supercapacitor, which will become a comprehensive environmental friendly energy storage device with both high energy density and high power density, to fundamentally solve the deficiency of the currently used portable energy storage/energy conversion device, and to reform the existing commercial energy devices.